As the wireless access network it is possible to use radio networks of public mobile phone systems, such as, for example, GSM, IS-54, IS-95, CDMA-2000 and WCDMA radio networks, as well as radio networks using unlicensed radio frequencies, such as, for example, a wireless local area network in its different forms (for example different versions of IEEE 802.11) and Bluetooth networks. The access networks can be used in both a circuit-switched mode (radio networks of public mobile phone systems) and a packet-switched mode (radio networks using unlicensed radio frequencies) for circuit-switched services (reference: UMA). UMA (Unlicensed Mobile Access) refers to a manner specified by the UMA consortium for relaying the circuit-switched signaling protocols of a public mobile phone system over a TCP/IP connection by utilizing, for example, any unlicensed radio frequency. The IP multimedia subsystem is a public mobile core network specified by 3GPP, with which multimedia services are produced to end users with wireless terminals compatible with the IP multimedia subsystem. The services of the IP multimedia subsystem are based on combinations of sound, images, data and text and they are used over a packet-switched transmission path and connection.
A central service of the IP multimedia subsystem will be an IP telephone service, which will implement, and possibly in the future also replace, conventional circuit-switched telephone services (i.e. teleservices) as well as supplementary services connected to them (i.e. call transfer, call holding/call pickup, etc.) in public mobile phone networks. However, a General Packet Radio Service (GPRS) in public mobile phone networks is not necessarily the best possible or the most cost-effective way to relay information requiring real-time, such as audio and video, over a wireless access network. In a core network a packet-switched transfer method based on data network protocols of prior art is a useful and cost-effective way to relay information requiring real-time, but for a wireless access network this is not the case, not necessarily even in access networks using unlicensed radio frequencies, when large numbers of users are involved. The packed-switched transfer method in wireless access networks of public mobile phone systems is designed especially for transferring narrow-band audio and video and it is the only audio in a wireless manner when large numbers of users are involved. This issue is discussed in 3GPP as well, where specification work for roaming packet-switched bearer services and IP multimedia subsystem session has been started.
Publications US 2003/0027569 A1, US 2003/0027595 A1 and US 2003/0026245 A1 disclose a system and a new entity (iMSC), by means of which the circuit-switched services of a public mobile core network can be implemented in the IP Multimedia Subsystem (IMS) specified by the 3GPP (3rd Generation Partnership Project). The publications disclose a new entity called iMSC, which converts the circuit-switched location updating and the voice service and feature control into SIP operations according to an IP multimedia subsystem. The publications do not directly describe how the conversion is performed, but they refer to known operation modes of a public mobile phone network and to the known operations of the elements of a public mobile phone system.
For example, the publications disclose that the iMSC performs registration of the user equipment (UE) in the IP multimedia subsystem, but they do not disclose which public user identity the iMSC registers in the IP multimedia subsystem for the user's terminal nor which address said public user identity is connected to by means of the address connection being registered. In accordance with the recommendations of the IP multimedia subsystem of 3GPP—to which the publications refer—there may be several registered public user identities and they may be in the form of a SIP resource identifier (SIP URI, Uniform Resource Identifier) or a uniform resource locator meant for a telephone number.
The above-mentioned public user identities are stored in an IP-multimedia-subsystem-specific subscriber identity module (SIM) card. If no public user identities are specified, one public user identity is derived according to the 3GPP recommendations from the International Mobile Subscriber Identity (IMSI) of the user, which is then registered in the IP multimedia subsystem. IMSI specifies the subscriber connection unambiguously, but IMSI is not a telephone number with which or to which it is possible to call from a conventional mobile phone or telephone network, and not necessarily even within the IP multimedia subsystem. In generic IP telephony networks the spectrum of public user identities is even wider, when proprietary systems, such as Skype, are also taken into account.
If now a mobile phone number is registered in the IP multimedia subsystem as the user's public address and the domain name of the iMSC as the address connection, as a person skilled in the art can assume from the operational descriptions of the publications in question and on the basis of the recommendations of 3GPP and IETF—and which is an absolute condition for the solution disclosed in the publications to even function—it still remains unclear how the address connection registered for the user is provided to the ENUM/DNS service. It is not specified in the recommendations of 3GPP or IETF either.
For the part of call control the operation of the conversion is described in FIG. 3 of the publications, where the operation of iMSC is described by two known elements ‘MSC Server’ and ‘P-CSCF’. A person skilled in the art can on the basis of the publications assume that reference is made to elements specified in the 3GPP recommendations and their operation, in which case it remains unclear how the conversion is made, because neither of the above-mentioned elements supports the conversion of call control signaling in any way as such, and in the publications in question the way the conversion is made is not specified as a new operation for said elements. Elsewhere in the publications it is disclosed that the iMSC behaves like a combination of a SIP User Agent, (SIP UA) and ‘P-CSCF’. Further, a person skilled in the art can on the basis of the publications assume that reference is made to elements specified in the 3GPP recommendations and their operation, in which case it remains unclear how, for example, the conversion of a call control signaling is made, because neither of the above-mentioned elements supports the conversion of call control signaling in any way as such according to the 3GPP recommendations, and in the publications in question the way the conversion is made is not specified as a new operation for said elements.
For the part of call control signaling a more operative combination would be, according to the 3GPP recommendations and imitating the publications in question, for example a combination of ‘MSCServer’-‘T-SGW’-‘MGCF’-‘B-CSCF’ or ‘MSC Server’-‘T-SGW’-‘MGCF’. The same applies for the conversion of circuit-switched supplementary services. For the part of SIP registration the above-mentioned combination of the SIP user agent and ‘P-CSCF’ would be more operative from the point of view of the SIP connection procedure, if the interface between iMSC and the ‘C-CSCF’ entity mentioned in the publications would, in accordance with the 3GPP recommendations, be Gm. The interface between iMSC and the ‘C-CSCF’ entity is now specified by a new interface ‘Mx’. In the publications the interface is specified as an interface using the SIP connection procedure according to the procedures of the IP multimedia subsystem, there are no other specifications for it and in the 3GPP recommendations the interface in question does not exist. In addition, the SIP user agent and ‘P-CSCF’ do not as such support the conversion of the location updating signaling in any way according to the 3GPP recommendations.
Further, in connection with the location updating of the mobile phone network and registration to the IP multimedia subsystem, FIG. 4 of the publications shows that the location updating to the mobile phone network is performed first and then the registration to the IP multimedia subsystem. This may lead to an unfortunate situation for the user: if the location updating to the mobile phone network is now successful, but registration to the IP multimedia subsystem fails, the result is a situation where no calls can be made with the terminal in question and no calls are received in it, because the user in question has not registered to a core network, i.e. the IP multimedia subsystem. The situation cannot be rectified until the terminal performs a periodic location updating or the user switches the terminal off and on again, in which case the registration to the IP multimedia subsystem is attempted again. In paragraph [0059] of the publication US 2003/0026245 A1, is mentioned the procedure ‘inter-iMSC Location Update’ of the 3GPP recommendation TS 24.008, which, however, is not specified in the recommendation in question, nor is, for example, the ‘inter-MSC Location Update’ procedure. The same procedure is mentioned in the other above-listed publications as well.
The publication mentions the iMSC entity performs the authentication of the user, for example paragraphs [0057] and [0059] of US 2003/0026245 A1, which on the basis of the description in the publication is an authentication based specifically on the procedures of a conventional mobile phone network, i.e. authentication performed by the visitor location register VLR on the basis of authentication parameters received from the home location register HLR over the MAP interface, and not an authentication performed by an IP multimedia subsystem. This assumption is also supported by the description of the operation in paragraph [0098] of US 200370026245 A1 (which description of operation can be found in the other publications as well): iMSC entity sends an SIP registration request to the ‘CSCF’ (first to ‘I-CSCF’, which sends the request further to ‘S-CSCF’), after which the ‘CSCF’s should perform authentication of the terminal through the iMSC entity by using the SIP authentication procedure of the IP multimedia subsystem and only then bring the SIP registration to a finish with ‘HSS’.